U.S. patent number 4,585,209 [Application Number 06/545,907] was granted by the patent office on 1986-04-29 for miniature valve and method of making same.
This patent grant is currently assigned to Harry E. Aine, Barry Block. Invention is credited to Harry E. Aine, Barry Block.
United States Patent |
4,585,209 |
Aine , et al. |
April 29, 1986 |
Miniature valve and method of making same
Abstract
In a miniature valve, a valve seat is formed by aperturing a
plate. A cantilever leaf spring is disposed overlying the apertured
plate for controlling the flow of fluid therethrough. An
electrostatic potential applied between the cantilever leaf spring
and the valve plate pulls the leaf spring over the apertured plate
for variably controlling flow through the valve in accordance with
the magnitude of the applied potential. In a preferred embodiment,
the cantilever leaf springs are made in batch form by etching a
silicon wafer. A flow controller is provided by measuring the
electrical capacitance of the valve, comparing it with a reference
voltage and deriving a feedback voltage applied to the valve for
controlling flow therethrough. In one embodiment, the width of the
cantilever leaf spring valve member is narrowed toward its free end
for finer control of flow.
Inventors: |
Aine; Harry E. (Los Altos,
CA), Block; Barry (Los Altos, CA) |
Assignee: |
Aine; Harry E. (Los Altos,
CA)
Block; Barry (Los Altos, CA)
|
Family
ID: |
24178010 |
Appl.
No.: |
06/545,907 |
Filed: |
October 27, 1983 |
Current U.S.
Class: |
251/129.02;
137/855; 251/298 |
Current CPC
Class: |
F15C
5/00 (20130101); F16K 31/02 (20130101); F16K
99/0001 (20130101); F16K 99/0007 (20130101); F16K
99/0057 (20130101); G05D 7/0694 (20130101); F16K
99/0051 (20130101); F16K 99/0034 (20130101); Y10T
137/7891 (20150401); F16K 2099/0074 (20130101); F16K
2099/008 (20130101) |
Current International
Class: |
F15C
5/00 (20060101); F16K 31/02 (20060101); G05D
7/06 (20060101); F16K 031/02 () |
Field of
Search: |
;251/129,141,298,131,138
;137/855 ;331/36R ;324/61R |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Jones; Larry
Attorney, Agent or Firm: Aine; Harry E.
Claims
What is claimed is:
1. In an electrostatic miniature valve;
valve seat means having an opening therein through which the flow
of fluid is to be controlled and having a valve seat electrode
portion for receiving an operating potential in use;
valve means for disposition adjacent said valve seat means and
having a cantilever leaf spring portion for overlaying said valve
seat means and said opening and also including a valve member
electrode portion mechanically operatively associated with said
leaf spring portion for receiving an operating potential in use;
and
electrical insulator means for disposition between said electrode
portion of said valve seat means and said valve member electrode
portion of said valve means, the mutually opposed areas of said
electrode portions and their spacings being dimensioned for
allowing an electrical potential difference to be applied between
said valve means and said valve seat means for pulling said
cantilever leaf spring portion by electrostatic attraction over
said opening in at least partially closing relation therewith for
controlling the flow of fluid therethrough.
2. The apparatus of claim 1 wherein said opening in said valve seat
means is of an elongated cross-section.
3. The apparatus of claim 2 wherein said cantilever leaf spring
portion of said valve means includes a free end portion for
disposition proximate a first end of said elongated opening and a
root portion for being fixedly secured relative to said valve seat
means and for disposition proximate the second end of said
elongated opening.
4. The apparatus of claim 3 including means for applying and for
varying an electrical potential applied between said valve means
and said valve seat means for variably controlling the flow of
fluid through said opening in said valve seat means.
5. The apparatus of claim 3 wherein said cantilever leaf spring
portion narrows in width toward the free end portion thereof.
6. The apparatus of claim 1 wherein said cantilever leaf spring
portion of said valve is a leaf spring having a major face thereof
facing said valve seat means.
7. The apparatus of claim 6 wherein said major face of said leaf
spring facing said valve seat means has an area overlaying said
valve seat means which is at least three times the cross-sectional
area of said opening of said valve seat facing said leaf
spring.
8. The apparatus of claim 7 including a sealing ridge disposed on
the face of said valve seat means facing said leaf spring and
encircling said opening in said valve seat means, said sealing
ridge being disposed proximate said opening.
9. The apparatus of claim 1 wherein said leaf spring is made of
silicon.
10. The apparatus of claim 1 wherein said insulator means is made
of silicon dioxide.
11. The apparatus of claim 1 wherein said valve seat means includes
an electrically conductive layer disposed on an electrically
insulative plate.
12. The apparatus of claim 1 wherein said electrical insulator
means includes a portion of an electrically insulative plate, said
plate being apertured to define said valve seat means.
13. The apparatus of claim 1 including:
means for measuring the capacitance of the valve between said
cantilever leaf spring portion and said valve seat means to derive
a positional output representative of the position of the
cantilever leaf spring portion relative to said valve seat
means;
means for comparing the positional output with a reference output
to derive a feedback control output voltage for application between
said cantilever leaf spring portion and said valve seat means for
controlling the position of the cantilever leaf spring portion of a
desired position.
14. In a method for making a miniature valve, the steps of:
etching a semiconductor wafer to define a cantilever leaf spring
structure free at one end and supported from a support structure at
the other end;
perforating a plate to define a valve seat area structure
encircling an aperture;
electrically insulating the cantilever leaf spring relative to said
valve seat;
disposing the cantilever leaf spring overlaying said aperture and
valve seat area; and
applying an electrical potential between said cantilever leaf
spring and said valve seat area of said plate underlying said leaf
spring for electrostatically pulling said leaf spring against said
valve seat area in fluid sealing engagement therewith for at least
partially limiting the flow of a fluid through said aperture.
15. The method of claim 14 wherein the step of perforating the
plate to define the valve seat area encircling the aperture
includes the step of, etching the aperture through a semiconductive
wafer.
16. The method of claim 14 wherein the step of electrically
insulating the cantilever leaf spring relative to the valve seat
includes the step of, growing on oxide layer on at least one of
said cantilever leaf spring and valve seat structures.
17. The method of claim 14 including the steps of:
measuring the capacitance of the valve between said cantilever leaf
spring and said valve seat to derive a positional output
representative of the position of the cantilever spring relative to
the valve seat; and
comparing the positional output with a reference output to derive a
feedback control output voltage for application between said
cantilever leaf spring and said valve seat for controlling the
position of the valve to a desired position as determined by the
reference output.
Description
BACKGROUND OF THE INVENTION
The present invention relates in general to miniature flow control
valves and, more particularly, to an improved miniature valve which
is variably controlled or closed via the application of an
electrostatic potential between the valve seat and the valve
member. In addition, the valve structure is readily fabricated by
batch semiconductor processing technology.
DESCRIPTION OF THE PRIOR ART
Heretofore, miniature variable control valves have typically
employed a valve seat with a ball valve member movable into and out
of sealing engagement with the seat by means of a solenoid or heat
applied to a thermal expansion member controlling the position of
the ball valve member.
One of the problems with such an arrangement is that it is
relatively bulky and requires that a substantial number of
individual parts be fabricated and assembled to form the valve.
It would be desirable to provide a miniature variable control valve
which has a minimum of parts and which is amenable to batch
fabrication type processes typically used in the semiconductive
industry.
SUMMARY OF THE PRESENT INVENTION
The principal object of the present invention is the provision of
an improved miniature flow control valve and method of making
same.
In one feature of the present invention, a cantilever leaf spring
overlies an apertured valve plate through which the flow of fluid
is to be controlled and an electrical potential is applied between
the valve plate and the cantilever leaf spring valve member for
pulling the valve member by electrostatic attraction over said
apertured plate in at least partially closing relation therewith
for controlling the flow through the apertured plate.
In another feature of the present invention, the apertured region
in the valve plate is elongated with the axis of elongation
extending away from the root portion of the cantilever spring
toward the free end portion thereof for facilitating variable
control of the flow through the apertured plate.
In another feature of the present invention, a sealing ridge
extends around the lip portion of the aperture in the apertured
plate to facilitate sealing of the valve member to the valve
seat.
In another feature of the present invention, the cantilever leaf
spring valve member is formed by etching a semiconductive wafer in
such a manner as to leave the cantilever leaf spring supported from
a support structure.
In another feature of the present invention, the area of the valve
leaf spring structure which overlies the valve seat structure is at
least three times the cross-section area of the apertured portion
of the valve plate, whereby relatively lower voltages may be
applied between the members for controlling the flow through the
valve.
In another feature of the present invention, the cantilever leaf
spring valve member is electrically insulated from the valve plate
via the intermediary of a layer of silicon dioxide grown on one of
the members.
Other features and advantages of the present invention will become
apparent upon a purusal of the following specification taken in
connection with the accompanying drawings wherein:
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a longitudinal cross-sectional view of a miniature flow
control valve incorporating features of the present invention,
FIG. 2 is a cross-sectional view of the structure of FIG. 1 taken
along line 2--2 in the direction of the arrows,
FIG. 3 is an enlarged detail view of an alternative to the valve
plate structure of FIG. 2 delineated by line 3--3,
FIG. 4 is an enlarged sectional view of the structure of FIG. 3
taken along line 4--4 in the direction of the arrows,
FIG. 5 is a view similar to that of FIG. 1 depicting an alternative
embodiment of the present invention,
FIG. 6 is a cross-sectional view of the structure of FIG. 5 taken
along 6--6 in the direction of the arrows,
FIG. 7 is a schematic circuit diagram, partly in block diagram
form, of a fluid flow controller incorporating features of the
present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to FIGS. 1 and 2, there is shown a miniature flow
control valve 11 incorporating features of the present invention.
The valve 11 includes a valve plate structure 12 having an aperture
13 formed therein through which the flow of fluid is to be
controlled. A cantilever leaf spring valve member 14 is disposed
overlaying the aperture 13 in the valve plate 12. The leaf spring
14 is joined at its root portion 20 to a surrounding support or
frame structure 15.
An electrically insulative layer 16 is provided between the frame
15, cantilever leaf spring 14, and the valve plate 12 for
electrically isolating the valve member 14 from the valve seat
region of the valve plate 12. An electrical potential, supplied
from a battery 17 or other source, is applied between the valve
member 14 and the valve plate 12 via the intermediary of the
potentiometer 18 and leads 19 making electrical connection to the
frame 15 and valve plate 12, respectively.
Sections of aligned gas flow tubing 21 and 22 are fixedly secured
to the adjoining faces of the valve plate 12 and frame 15,
respectively. In a typical example, the aligned sections of tubing
21 and 22 are fixed to the respective members 12 and 15 via the
intermediary of a suitable adhesive as of epoxy. After the frame 15
and valve plate 12 have been held together and joined to the
adjoining sections of flow tubing 21 and 22, the assembly is potted
with a suitable potting material 23 such as a relatively rigid
electrically insulative plastic material.
In operation, fluid tubing 21 is connected to a source of fluid
under pressure, the flow of which is to be controlled via the valve
11. The potentiometer 18, for full flow conditions, is adjusted for
zero potential difference between the cantilever leaf spring valve
member 14 and the valve seat region underlying the cantilever
spring 14. The fluid pressure exerted on the cantilever leaf spring
causes the leaf spring to be deflected as indicated by the dotted
lines of FIG. 1. This, then, represents the full flow position of
the control valve 11.
The flow is then adjusted to a desired limited value by adjusting
the setting of the potentiometer 18. As the potential applied to
the valve 11 is increased, electrostatic attractive forces between
the valve seat region and the valve member 14 cause an increasing
proportion of the flow aperture 13 to be closed off. The closing
action begins proximate the root end of the cantilever spring valve
member 14 and progresses with increasing potential toward the free
end of the cantilever spring 14.
The insulative material 16 and its thickness are chosen such that
the required electrostatic force is obtained for closure of the
valve without exceeding the dielectic strength of the insulative
layer 16. Also, the thickness of the cantilever spring 14 is chosen
such that in the absence of an applied potential, the desired flow
rate is obtained through the opening 13. With relatively thin
layers of good dielectric strength insulative material 16, such as
silicon dioxide and silicon nitride in thicknesses from 1,000 .ANG.
to 10,000 .ANG., relatively low operating voltages may be employed
in the range of five to 100 volts. In a typical example, the valve
11 is dimensioned to fit inside a standard 1/4" o.d. tubing 21 and
22.
The flow control valve 11 is conveniently fabricated in batch form
by chemically etching a silicon wafer. More particularly, the frame
15 and valve member 14 are conveniently formed by anisotropically
etching a silicon wafer from one major face and terminating the
etch on an etch stop layer deposited on the other major face of the
wafer to a thickness corresponding to the desired thickness of the
cantilever spring valve member 14. In a typical example, the etch
stop layer may comprise a layer of n-type conductivity silicon
material on a P-type substrate to provide an electro-etch stop with
a passivating potential of plus 0.5 volts applied to the n layer
relative to the etchant electrolyte (KOH). This is disclosed in
U.S. Pat. No. 3,689,389 issued Sept. 5, 1972. As an alternative,
the etch stop layer may be doped to a suitable dopant concentration
of P material such as greater than 5.times.10.sup.19 per cubic
centimeter and used as a concentration stop with a suitable etchant
such as ethylene diamine, pyrocatechol (E.D.P.). In still another
alternative, the etch stop layer may be silicon dioxide grown on
the substrate wafer and rendered conductive for the purposes of
electrostatic attraction by means of an electrically conductive
layer deposited on the face thereof facing the valve seat. A
suitable, electrically conductive material would be gold deposited
to a thickness of 5,000 .ANG. over 500 .ANG. of TiW. Silicon
dioxide is a good etch stop layer for the anisotropic etchant
E.D.P.
The silicon valve plate 12 is conveniently apertured (perforated)
by anyone of the aforecited anisotropic etchants for etching
silicon. The mutually opposed faces of the wafers which are to form
the valve seat and cantilever valve member 14, are polished
surfaces of silicon wafers as of mirror finish.
Referring now to FIGS. 3 and 4, there is shown an alternative
embodiment of the present invention wherein a sealing ridge 25, as
of 1 to 5 microns in height and 2 to 3 mils in width, is formed
encircling the flow aperture 13. This ridge is conveniently formed
by masking and etching the major face of the wafer to leave the
ridge portion 25. The sealing ridge 25 facilitates the formation of
a gas-tight seal by being pressed into firm sealing engagement with
the leaf spring member 14 by the pull of electrostatic attraction
between the leaf spring 14 and the underlying valve seat region of
the valve plate 12.
Referring now to FIGS. 5 and 6, there is shown an alternative
embodiment of the present invention. More particularly, the
miniature flow control valve assembly 26 includes an apertured
valve plate 27 of an electrically insulative material, such as
glass sold under the trademark "PYREX" commercially available from
Corning Glass as 7740 glass. Pyrex glass plate 27 is suitably
apertured with a linear array of circular openings 28 formed by
laser drilling. As an alternative, the Pyrex glass plate may be
etched with a suitable HF etchant to provide a rectangular opening
similar to that of 13 in the embodiment of FIGS. 1 and 2.
The valve seat surface of the major face of the valve plate 27 is
coated with a suitable electrically conductive material as of gold
to a thickness of 5,000 .ANG. deposited over 500 .ANG. of Cr. The
conductive layer is then patterned to provide a valve seat
electrode 29 which is to underlie the cantilever valve spring 14.
The electrode 29 is connected to contact pad 31 via a lead portion
32 of the metallization layer forming the electrode 29.
The cantilever leaf spring valve member 14 and surrounding frame
portion 15 are essentially identical to that previously described
with regard to FIGS. 1 and 2. However, an insulative layer 30 is
deposited on the face of the cantilever leaf spring portion 14
which faces the valve plate 27. This serves to electrically
insulate the cantilever leaf spring valve member 14 from the valve
seat electrode 29. The electrically insulative layer formed on the
valve member 14 is conveniently formed by growing a silicon dioxide
layer on the major face of the silicon wafer which is to form the
frame and valve member and then selectively patterning the oxide by
a suitable oxide etchant such as buffered HF. The pattern removes
the oxide from the regions of the wafer other than those of the
valve member 14. Again, the mutually opposed faces of the silicon
wafer and Pyrex glass plate 27 are polished surfaces and the
silicon wafer is bonded overlaying the glass wafer 27 by anodic
bonding.
The silicon frame member 15 includes a notched portion overlaying
the contact pad 31 to provide access to the underlying pad 31.
After the glass and silicon wafers have been bonded together, the
individual valves 26 may be tested while the assembly is still in
wafer form. Thereafter, the composite wafer is diced into
individual valve assemblies 26 by conventional sawing techniques
employing a saw tape extending over the opposite major faces of the
composite bonded assembly so as not to introduce contaminants into
the valve mechanisms. Thereafter the bonded valve assemblies are
positioned between the flow tube segments 21 and 22 and potted in
place as previously described with regard to FIGS. 1 and 2.
The advantage to the miniature flow control valve of the present
invention is that it is amenable to batch fabrication utilizing
silicon semiconductor processing technology, thereby reducing its
cost of manufacture. In addition, it allows, the valve size to be
reduced to a minimum and permits a relatively low voltage to be
employed for variably controlling the flow through the valve. Since
the operation of the valve is electrostatic, it consumes
essentially no power.
In an alternative embodiment of the cantilever leaf spring valve,
as shown by phantom lines 40 of FIG. 6, the width of the cantilever
leaf spring 14 is narrowed toward the free end of the cantilever
leaf spring. This will decrease the strength of the spring bias
near the free end of the spring. Thus, it will require additional
electrical potential to achieve the same degree of closure of the
valve. As a result, a finer control is obtained over the low flow
regime of the valve than that obtained by the rectangular valve
14.
As thus far described, the miniature control valve has used an
electrostatic potential for controlling the amount of closure of
the valve. This is not a requirement. The miniature valve may be
used without the applied potential and thus, without the insulator
16, relying on the spring constant of the leaf spring 14 for
providing a restoring force or closure force on the valve. In this
configuration, the valve would operate as a check valve allowing
flow in only one direction. Reverse flow would produce closure of
the valve.
Referring now to FIG. 7 there is shown a fluid flow controller 35
incorporating features of the present invention. The capacitance of
the valve 11 is connected in one arm of a bridge circuit 36
including a reference capacitor 37 and a pair of resistors 38 and
39. The bridge circuit 36 is excited with a radio frequency
voltage, at say 10 KHz, from an oscillator 41 feeding opposite
terminals of the bridge 36 through the intermediary of d.c.
isolating capacitors 42 and 43. Reference capacitor 37 has a value
of capacitance equal to the capacitance of the valve 11 at its
fully open position. Resistors 38 and 39 have a value of resistance
such as to balance the reactive impedance of the valve capacitance
and reference capacitance 37 such that the bridge 36 is balanced at
the selected valve fully open position.
The output from the bridge is coupled via coupling (d.c. isolating)
capacitors 44 and 45 into one input of a phase sensitive detector
46. Phase sensitive detector 46 phase detects the bridge unbalance
signal against a reference voltage derived from the R.F. oscillator
41 over line 47. The output of the phase sensitive detector 46 is a
d.c. voltage corresponding to the degree to which the valve is
closed.
A calibrated source of flow reference voltage applied at terminal
48 is compared in a comparator 49 with the measured capacity
voltage derived from the bridge via phase sensitive detector 46.
The output of the comparator 49 is a voltage of a magnitude
necessary to bring the measured position of the valve 11 into
coincidence with the desired or reference position of the valve 11
as determined by the flow reference voltage at terminal 48.
The d.c. output voltage of the comparator 40 is feedback via line
51 to the valve 11 so as to cause the valve to close in proportion
to the reference voltage 38. Knowing the fluid pressure head
supplied to the valve 11, the flow reference voltage may be
calibrated in terms of desired flow rate. In this manner, setting
of the flow reference voltage will cause the valve 11 to close to
such a position as to yield the desired flow rate.
* * * * *